feat: add visual Graph Builder tool to Burr UI

[skrawcz]

This takes work from @jaeyow and #572.

Adds a drag-and-drop graph editor for designing Burr application graphs visually and exporting as Python code or JSON.

Changes

• these are UI only changes to add new graph-builder

Key changes:

• New /graph-builder route with full visual editor (ReactFlow v12)
• Migrate existing GraphView from reactflow v11 to @xyflow/react v12
• Remove reactflow and @tisoap/react-flow-smart-edge dependencies
• Per-node async/streaming toggles matching Burr's 4 action variants
• Python code generation with correct decorators and signatures
• 3 pre-built example graphs (MultiModal Chatbot, CRAG, Streaming)
• localStorage auto-save/restore of graph state
• Empty-state onboarding overlay and structured help sidebar
• Fix appcontainer layout for full-height content

How I tested this

• locally

Notes

Next would be to unify the color schemes with the observability components.

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[github-actions]

A preview of b71f715 is uploaded and can be seen here:

✨ https://burr.dagworks.io/pull/667 ✨

Changes may take a few minutes to propagate. Since this is a preview of production, content with draft: true will not be rendered. The source is here: https://github.com/apache/burr/tree/gh-pages/pull/667/

[skrawcz]

Nice, self-contained addition — the Graph Builder is cleanly factored (separate exporter / code-generator / loader / presentational components), every new file carries the Apache header, and the generated Python correctly matches Burr's real API including the async-streaming AsyncGenerator[Tuple[dict, Optional[State]], None] signature. The reactflow v11 → @xyflow/react v12 migration looks correct (edgesUpdatable→edgesReconnectable, named ReactFlow import, updated CSS path) and nets a dependency reduction with no impact on the burr package, so backwards compatibility is fine.
Before merge I'd like to see:

1. Unit tests for BurrCodeGenerator, GraphExporter, and ExampleLoader.validateExample — these are pure functions and the highest-value thing missing. At minimum, assert validateExample returns [] for each bundled example and snapshot the generated Python for one sync + one streaming graph.
2. Fix the duplicate-label code-generation bug: deduplicateNames is applied only to the with_actions list, not to the generated defs or transitions, so two nodes with the same label produce colliding/redefined functions. Dedup consistently or key off node.id.
3. A short docs page (the PR checklist docs item is unchecked) and a manual smoke-test of existing UI pages given the shared appcontainer layout change and the v12 migration.
   Also worth a quick confirmation: dropping the smart-edge routing in favor of plain bezier paths in the observability GraphView is a minor visual regression (edges may cross nodes) — is that acceptable?

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Inline notes (line refs approximate — folded into body since this is a body-only draft):

• File: telemetry/ui/src/components/routes/graph-builder/utils/BurrCodeGenerator.ts
  Line: ~148 (generateGraphFunction — deduplicateNames call)
  [BLOCKING] deduplicateNames is applied here to build the with_actions(...) list, but generateActions and generateTransitions call sanitizeNodeName(node.label) directly with no dedup. Two nodes sharing a label therefore produce two identically-named defs and ambiguous transition strings — invalid Python. Please dedup consistently across function definitions, the action list, and transitions (or key generation off the stable node.id rather than the display label).
• File: telemetry/ui/src/components/routes/graph-builder/utils/BurrCodeGenerator.ts
  Line: ~106 (getInputParameters)
  [SUGGESTION] Input parameter names aren't deduplicated, so two input edges resolving to the same sanitized name would emit duplicate function parameters (a SyntaxError). Cheap to guard with the same dedup logic.
• File: telemetry/ui/src/components/routes/graph-builder/utils/GraphExporter.ts
  Line: ~57 (metadata.created: new Date().toISOString())
  [SUGGESTION] This runs inside the useMemo recomputed on every node/edge change and is written to localStorage, so created resets to "now" on every edit. Set it once at creation (or omit from the persisted blob) — this also makes the generated JSON snapshot-testable.
• File: telemetry/ui/src/components/routes/graph-builder/utils/ExampleLoader.ts
  Line: ~52 (validateExample)
  [SUGGESTION] Great that this validator exists — please wire it into a unit test that runs over each bundled ExampleGraph and asserts it returns [], so a malformed example can't ship silently.
• File: telemetry/ui/src/components/routes/app/GraphView.tsx
  Line: ~170 (removal of getSmartEdge, replaced by getBezierPath)
  [NIT] Dropping smart-edge routing is a minor visual regression for the observability graph (edges may overlap nodes). Fine if intentional given the dependency removal — just calling it out for confirmation.
• File: telemetry/ui/src/components/nav/appcontainer.tsx
  Line: ~394 (<main> layout rewrite)
  [NIT] This changes the shared layout used by every route (removing the previous py-14 -my-1 margins for a flex column). Reasonable cleanup, but please smoke-test existing pages (projects, app view, annotations) for spacing regressions since it's outside the graph-builder scope.
• File: telemetry/ui/src/components/routes/graph-builder/components/GraphBuilder.tsx
  Line: ~230 (useEffect(..., []) initial-load hook with eslint-disable)
  [NIT] The mount-only load effect disables exhaustive-deps. Acceptable for a one-time restore, but a brief comment on why (avoid re-running on initialGraph/loadGraphIntoCanvas identity changes) would help future readers.

[skrawcz]

Need to remember whether relationship with #687 means this is required or superseded

[skrawcz]

need to rebase this against vite changes